The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines combust an air/fuel (A/F) mixture within cylinders to drive pistons that turn a crankshaft and generate drive torque. Homogeneous charge compression ignition (HCCI) engines may operate in different modes. For example, the engine may operate in a conventional spark-ignition (SI) combustion mode or various HCCI combustion modes including an HCCI combustion mode and a mixed HCCI combustion mode. In the SI combustion mode, the A/F mixture within the cylinders is compressed and ignited via spark from spark plugs. In the HCCI combustion mode, the A/F mixture is compressed until the A/F mixture self-ignites. For example, the A/F mixture may automatically combust after exceeding a critical pressure or temperature threshold. The HCCI combustion mode, however, is more difficult to control than the SI combustion mode and therefore may be limited to use during particular operating conditions.